CA125 is a well-recognized marker for endometrial cancer. Uterine malignant mixed müllerian tumors (MMMTs) are increasingly being recognized as an aggressive adenocarcinoma, not a sarcoma. There are no data in the literature regarding CA125 in this malignancy. One hundred twelve women with surgically staged MMMT, diagnosed between July 1990 and September 2005, had a retrospective chart review performed. Preoperative CA125 levels were available in 29 (26%) women. Seventeen (49%) women had levels above the upper limit of normal of 35 kmicro/L. Mean levels increased with increasing surgical stage: stage I 53.4 kmicro/L; stage II 122.5 kmicro/L; stage III 147.1 kmicro/L; and stage IV 428.4 kmicro/L. Elevated levels of CA19-9, CEA, and CA15-3 were found in 8%, 12%, and 25%, respectively.